Biomedical Engineering Reference
In-Depth Information
and original and secondary beam number used for the simulation are stan-
dard values obtained from Boston Sci. [24]. However, the optimal values of
frequency and attenuation coefficient are obtained by the cross validation pro-
cedure [23]. The dimensions, scatterer number, and the backscattering cross-
section of the simulated arterial structures were obtained from different lit-
erature [7, 10, 11, 19, 22, 24]. Typical values of the RBCs “voxel” numbers took
into account the typical hematocrit percentage [11] (Section 1.4.4). Instrumen-
tal and video noise has been incorporated into the simulated image, due to
electronics acquisition data, and the acquisition and processing to the video
format.
The zones of greater medical interest (lumen, lumen/intima, intima/media,
and media/adventitia) were simulated for several real IVUS images. The smooth-
ing image protocol is not known so that the corresponding tests were done until
the maximal similarity to the real images was found, based on the use of three
progressive methods. (1) The empty pixels are filled using the average of eight
neighbors, (2) a median filter is used, and (3) a Gaussian filter is applied in or-
der to find the noise reduction. The quantitative parameters used for the image
comparison were directed for global and local image regions, and are described
below.
1.
Gray-level average projections p
x
and p
y
, that is horizontal and vertical
image projections, are defined for an
m
×
n
image
I
as [25]:
m
n
1
m
1
n
p
x
(
i
)
=
I
ij
,
p
y
(
j
)
=
I
ij
(1.16)
j
=
1
i
=
1
2. We define a global linear
correlation
between real (
x
) and simulated (
y
)
data as follows:
y
=
mx
+
b
(1.17)
where
m
and
b
are the linear correlation coefficients.
3.
Contrast to noise ratio signal
(CNRS) as figure of merit, defined as [26]:
(
µ
1
−
µ
2
)
2
CNRS
=
(1.18)
2
1
+
σ
2
2
σ
where
µ
1
,
µ
2
,
σ
1
, and
σ
2
are the mean and the standard deviations inside
the ROIs.
